Steffen Gielen

Research Interests

Our current understanding of cosmology is that the Universe began at the Big Bang; the Big Bang itself is a singularity, where general relativity breaks down. This breakdown motivates the search for quantum gravity; the fact that our Universe seems to have started in a singularity gives observational relevance to this search: a theory that resolves the Big Bang singularity should make cosmological predictions.

The aim of my research is to develop new models for the early Universe, which connect quantum gravity to cosmology, demanding that these resolve the singularity problem. Doing this strengthens the theoretical foundations of modern cosmology, and can provide observational tests for quantum gravity.

I am currently working on two scenarios in which quantum effects replace the Big Bang singularity by a non-singular "bounce". The first scenario starts from group field theory, a non-perturbative approach to quantum gravity in which space and time themselves emerge from discrete quantum structures that form a "condensate". The second scenario uses semiclassical methods in quantum cosmology to describe the passage through the bounce as akin to quantum-mechanical tunnelling; one can directly calculate the transition of cosmological perturbations through the bounce.

Exploration of these complementary directions should shed light on what aspects of quantum gravity lead to a consistent theory of singularity resolution; this is particularly important in light of the growing interest in a variety of different bounce scenarios (as discussed in a successful workshop at Perimeter in June 2017).